Date: Thu, 21 Dec 1995 16:25:10 -0500 From: tsingle@sunland.gsfc.nasa.gov (Tim Singletary) To: hackers@freebsd.org Subject: semctl() portability issue and fix Message-ID: <199512212125.QAA10262@sunward.gsfc.nasa.gov.gsfc743>
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FreeBSD 2.1, in /usr/include/sys/sem.h declares
int semctl __P((int, int, int, union semun));
Note that the fourth argument to semctl() is required. Other unix
systems (SunOS, Solaris, HPUX, and OSF1, to name a few) treat the
fourth argument as optional unless the third argument is SETVAL,
GETALL, SETALL, IPC_STAT, or IPC_SET. The SunOS manual
_Porting_Software_to_SPARC_ even says:
Programs that call semctl() with these subcommands [those
requiring a fourth argument] must pass the union itself, rather
than an element of the union, or a constant such as 0 (zero).
Programs that call semctl() with other subcommands should omit the
fourth argument, rather than pass a constant such as 0 (zero).
So there's a portability issue: code which compiles and runs just
fine on other systems won't compile on FreeBSD!
I've `fixed' things so that the fourth argument is optional on my
system. My fix ignores the ``#if __STDC__'' wrapper in the original
semctl.c -- won't it always get compiled in a `__STDC__'
environment?
Anyway, here's what I've done:
1: I changed line 164 of /usr/include/sys/sem.h from
int semctl __P((int, int, int, union semun));
to
int semctl __P((int, int, int, ...));
2: I replaced /usr/src/lib/libc/gen/semctl.c with
-begin--------------
#include <stdarg.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semctl(int semid, int semnum, int cmd, ...)
{
va_list ap;
union semun fourth_arg;
union semun *fourth_arg_ptr;
va_start(ap,cmd);
if (cmd == IPC_SET || cmd == IPC_STAT || cmd == GETALL
|| cmd == SETVAL || cmd == SETALL) {
fourth_arg = va_arg(ap, union semun);
fourth_arg_ptr = &fourth_arg;
}
fourth_arg_ptr = NULL;
va_end(ap);
return (semsys(0, semid, semnum, cmd, fourth_arg_ptr));
}
-end----------------
Anyway, I'd appreciate all comments! Naturally, I'd like to see this
(or some other fix) make its way into the FreeBSD source tree.
tim
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